The object of the invention is a method for forming a data transfer connection between a data transfer system and a subscriber device, terminal equipment and a data transfer system wherein at least two subscriber devices are connected to one subscriber connection of the data transfer system. The invention can be preferably applied, for example, in Wireless Local Loop networks, i.e. WLL networks.
WLL systems are a preferable way to extend the public switched telephone network to new subscribers since the extension can be carried out without having to provide cabling for each subscriber separately. In wireless local loop networks, i.e. WLL networks, the terminal equipment which are in use comprise a telephone or some other subscriber station which is suitable for connecting to the public switched telephone network and a tranceiver unit connected to it. The adaptation between the subscriber station and the tranceiver unit is executed by a line adapter. The tranceiver unit is usually connected by radio to a cellular service, which could be, for example, to a GSM system. It is often desirable to use one subscriber connection both for speech transmission and for transmission of character based data, such as telefaxes. There are, however, problems associated with this, especially in WLL systems, and they will be described more closely in the following.
In the following, the prior art is presented by describing first in some detail WLL terminal equipment according to the prior art and its connection to the data transfer system and by describing subsequently a solution according to the prior art for connecting two subscriber stations to the WLL data transfer system.
FIG. 1 shows a prior known solution for the implementation of a WLL terminal equipment. The WLL terminal equipment 100 is connected to a cellular system which comprises base stations 151 for transferring data by radio via an antenna 150 to terminal equipment. The base stations are connected to base station controllers 152 which are further connected to a switching center 153. The switching center 153 is linked to the public switched telephone network PSTN. Also a home location register HLR is connected to the switching center. The data concerning the subscribers of the system is stored to this register.
Terminal equipment 100 comprises an antenna 104 for transmitting and receiving a radio frequency signal. The received signal is amplified and demodulated into a baseband signal in an RF part 113 and the baseband signal is processed in a signal processing block 114 of the baseband part 110. Similarly, the transmitted baseband signal is processed for transmission according to specifications of the cellular system in block 114 and modulated into an RF frequency and amplified in the RF part 113 to be fed to the antenna 104.
The signal processing and the RF part are controlled by a processor 111 to which a memory 112 is connected for storing programs and parameters. A regulator 115 forms the supply voltages for the baseband part and for the RF part.
A line adapter part 130 comprises an audio part 134 for adapting the audio signal of the baseband part 110 and the audio signal of the telephone set to each other. A DTMF detector 133 detects dialling signals which are transferred in the audio line and transmits them to the processor 131 of the line adapter part. A HOOK detector 135 detects the state of the hook switch of the telephone device and transmits the status mode data to the processor 131 and to a tone generator 136. The tone generator 136 forms audio signals to the telephone on the basis of the status mode data of the connection which have been transmitted by the cellular system. A ringing generator 137 forms a high voltage ringing signal (for example, 45 V AC) for the ringing function of the telephone set. Voltage between lines/loop current (for example, 40 V DC) is formed in a DC regulator 138 to meet the specifications of the telephone set from the high voltage formed by a DC/DC converter block. The processor 131 controls the blocks of the line adapter and it is connected to the processor 111 of the mobile station part 110, for example, through serial bus. The program of the processor and the parameters connected to the functions of the line adapter and the status mode data of the connection are stored into a memory 132 connected to the processor 131.
The above presented solution according to the prior art has been described in more detail in the patent specification U.S. Pat. No. 5,117,450 (WO 9014729). Other WLL systems according to the prior art have been described, for example, in the patent specifications U.S. Pat. Nos. 4,658,096, 4,775,997 and 4,922,517.
It is often desirable to use one subscriber connection of the telephone both for speech transmission and for the transmission of character based data, such as telefaxes. The simplest method in this case is to connect in parallel a telephone set and, for example, a telefax to the same subscriber line. However, with respect to this arrangement the problem arises in the context of an incoming connection, since one does not know whether it is a phone call or a telefax transmission. In this case, one has to answer the phone and if it is concluded from the audio signals that it is a telefax transmission, the telephone receiver is set on-hook and the receiving function of the telefax is switched on. However, this demands that there is someone next to the telephone set monitoring all incoming connections. If the person is not present, the telefax has to be connected to an auto answer mode and thus only telefaxes can be transmitted to the subscriber connection. In this case, it is not possible to use, for example, a telephone answering machine parallel with the telefax. The telefax can also be used in an auto answer mode constantly but then, as an ordinary call is coming to the subscriber connection, the telefax feeds a disturbing audio signal to the line until the receiver notices that it is not a telefax transmission and receives the call by using the telephone.
To solve the above mentioned problem, two separate subscriber connections are often used, one for the telephone and the other for the telefax. FIG. 2 shows a prior known solution like this. A telephone 201 has been connected to the first WLL connection and a telefax 202 has been connected to the second WLL connection. For each connection there is a separate connection device 210, 220 which comprises an antenna 214, 224, an RF part 213, 223, a baseband part (BB) 212, 222, a line adapter (LA1, LA2) 211, 221 and an interface for connecting the subscriber station (INTERFACE 1, INTERFACE 2). However, the disadvantage of this solution is that the acquiring and upkeep of several subscriber connections leads to considerable costs.
The above mentioned disadvantages can be reduced by a prior known incoming call type recognition. The device answers the call automatically and receives the signal from the line for a maximum predetermined time. If it is a telefax transmission, the device detects the audio signal of a transmitting telefax and connects the line to the telefax. If, instead, during the predetermined time the device does not detect the audio signal of a telefax, it connects the line to the telephone. The problem with this kind of combination device is, however, that in the context of an ordinary call the device answers the incoming connection even though there is no one present to answer the call. In this case, connecting the line uses unnecessarily the capacity of the data transfer network and causes unnecessary costs to the caller. This is a special problem with the WLL connection since the capability of the WLL network to transmit connections in the communications channel is usually lower than the number of connections in the network in which case the forming of unnecessary connections may cause a network overload.
With the WLL network, there are also disadvantages associated with solutions according to the prior art that relate to outgoing connections. In this case, the WLL network has to recognize the type of the outgoing connection by waiting for a possible signal given by the telefax. This causes an extra delay in the forming of the connection. Particularly with long distance connections, when it may take a long time to form a connection in any case, this extra delay may exceed a time-out limit in the telefax. Exceeding time-out limit means that the telefax interprets the formation of the outgoing connection as having failed and closes the line.
The aim of the present invention is to devise a solution by means of which the above presented problems of the prior art can be avoided.
One idea of the invention is that information concerning subscriber stations, which have been connected to the subscriber connection, is stored in the data transfer system. This data is exploited for switching the incoming connection to the correct subscriber station and for setting the data transfer procedure of the outgoing connection quickly to correspond to the subscriber station being used.
Digital data transfer system is applied in the solution according to the invention to preferably allow one, on one hand, to exploit the possibility to refer to the subscriber indirectly by using the IMSI (International Mobile Subscriber Identity) identifier and, on the other hand, to exploit data concerning the parameters of the connection which is exchanged in the signalling between the terminal equipment and the data transfer system. In this case, the subscriber obtains for his/her use at least two connection identifiers, one of which can be considered as being for the telefax connection and one for the speech connection. Incoming connections are thus directed in the WLL terminal equipment to the telephone or to the telefax on the basis of the parameter information transferred in the signalling.
By means of the invention, it is possible to implement several subscriber station connections with WLL terminal equipment which has just one RF and baseband part in which case the costs of the purchase and upkeep of the subscriber connection can be reduced. In addition, it is possible to form a connection without unnecessary delay or requiring any manual operation. By means of the invention, also unnecessary formation of incoming speech connection can be avoided, if there is no person present to answer the call.
A method according to the invention for forming a connection between a data transfer system and a subscriber station wherein said subscriber station is one of at least two subscriber stations which are connected to the subscriber connection of the data transfer system, is characterized in that subscriber station information according to the subscriber connection and concerning subscriber stations connected to the subscriber connection is stored in the data transfer system, and the connection is formed depending on said subscriber station data.
Terminal equipment connected to a subscriber connection of a data transfer network according to the invention wherein the terminal equipment comprises interfaces for at least two subscriber stations, is characterized in that the terminal equipment comprises means for storing subscriber station information which is logically connected to the subscriber stations which have been connected to the terminal equipment and means for forming a connection between the subscriber station and the data transfer system depending on said subscriber station information.
A data transfer system according to the invention which comprises a subscriber connection to which at least two subscriber stations are connected, is characterized in that the data transfer system comprises the means for storing subscriber station information concerning subscriber stations which are connected to said subscriber connection and means for forming a connection between the data transfer system and a subscriber station which is connected to said subscriber connection depending on said subscriber station information.
Preferable embodiments according to the invention have been presented in dependent claims.